The present invention relates to conditioning polishing pads used in mechanical and/or chemical-mechanical planarization of microelectronic-device substrate assemblies. More particularly, the invention relates to retarding deterioration of conditioning elements and reducing contamination of polishing pads.
Mechanical and chemical-mechanical planarizing processes (collectively xe2x80x9cCMPxe2x80x9d) are used in the manufacturing of microelectronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic-device substrate assemblies. FIG. 1 schematically illustrates a planarizing machine 10 with a circular platen or table 20, a first carrier assembly 30, a polishing pad 40 having a planarizing surface 42, and a planarizing fluid 44 on the planarizing surface 42. The planarizing machine 10 may also have an under-pad 25 attached to an upper surface 22 of the table 20 for supporting the polishing pad 40. In many planarizing machines, a drive assembly 26 rotates (arrow A) and/or reciprocates (arrow B) the table 20 to move the polishing pad 40 during planarization.
The first carrier assembly 30 controls and protects a substrate assembly 12 during planarization. The first carrier assembly 30 typically has a carrier head or substrate holder 32 with a pad 34 that holds the substrate 12 to the carrier head 32. A drive assembly 36 typically rotates and/or translates the carrier head 32 (arrows C and D, respectively). The carrier head 32, however, may be a weighted, free-floating disk (not shown) that slides over the polishing pad 40.
The polishing pad 40 and the planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate assembly 12. The planarizing machine 10 can use a fixed-abrasive polishing pad having a plurality of abrasive particles fixedly bonded to a suspension material. The planarizing solutions 44 used with fixed-abrasive pads are generally xe2x80x9cclean solutionsxe2x80x9d without abrasive particles because an abrasive slurry may ruin the abrasive surface of fixed-abrasive pads. In other applications, the polishing pad 40 may be a nonabrasive pad composed of a polymeric material (e.g., polyurethane), a resin, or other suitable materials without abrasive particles. The planarizing solutions 44 used with nonabrasive polishing pads are typically xe2x80x9cslurriesxe2x80x9d that contain abrasive particles.
CMP processes should consistently and accurately produce a uniformly planar surface on the substrate assembly 12 to enable precise fabrication of circuits and photo-patterns. For example, during the fabrication of transistors, contacts, interconnects and other components, many substrate assemblies develop large xe2x80x9cstep heightsxe2x80x9d that create a highly topographic surface across the substrate assembly 12. To enable the fabrication of integrated circuits with high densities of components, it is necessary to produce a highly planar surface at several stages of processing the substrate assembly 12 because non-planar surfaces significantly increase the difficulty of forming submicron features. For example, it is difficult to accurately focus photo-patterns to within tolerances of 0.1 xcexcm on nonplanar surfaces because submicron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes often transform a topographical surface into a highly uniform, planar surface.
In the competitive semiconductor industry, it is also highly desirable to have a high yield of operable devices after CMP processing. CMP processes should thus quickly remove material from the substrate assembly 12 to form a uniformly planar surface at a desired endpoint. For example, when a conductive layer on the substrate assembly 12 is under-planarized in the formation of contacts or interconnects, many of these components may not be electrically isolated from one another because undesirable portions of the conductive layer may remain on the substrate assembly 12. Additionally, when a substrate assembly 12 is over-planarized, components below the desired endpoint may be damaged or completely destroyed. Thus, to provide a high yield of operable microelectronic devices, CMP processes should quickly remove material until the desired endpoint is reached.
To provide consistent results and produce planar surfaces, one aspect of CMP processing is maintaining the condition of the planarizing surface 42 on the polishing pad 40. The condition of the planarizing surface 42 changes because residual matter collects on the planarizing surface 42 of the polishing pad 40. The residual matter, for example, can be from the substrate assembly 12, the planarizing solution 44 and/or the polishing pad 40. In certain applications, residual matter from the substrate assembly 12 can even glaze over sections of the planarizing surface 42 (e.g., planarizing doped silicon dioxide layers). The substrate assemblies can also wear depressions into the planarizing surface 42 that create a non-planar planarizing surface. In many CMP applications, therefore, polishing pads are accordingly xe2x80x9cconditionedxe2x80x9d periodically to bring the planarizing surface into a desired condition for planarizing the substrate assemblies.
To condition the planarizing surface 42, the planarizing machine 10 can include a conditioning system 50 that rubs an abrasive conditioning stone 60 against the planarizing surface 42 of the polishing pad 40 between planarizing cycles. The conditioning stone 60 typically includes a metal plate 62, a layer of nickel 64 covering the bottom surface of the metal plate 62, and a plurality of diamond particles 66 embedded in the nickel layer 64. The metal plate 62 is attached to a second carrier assembly 70 that presses the diamond particles 66 against the polishing pad 40 and sweeps the conditioning stone over the planarizing surface 42.
One problem with conventional conditioning stones 60 is that they wear out and can adversely affect the conditioning of the polishing pad 40. Conventional conditioning stones, for example, may contaminate the planarizing surface 42 with material from the nickel layer 64 or the diamond particles 66. The nickel layer 64 may wear during the conditioning cycle, which leaves residual nickel on the planarizing surface 42 and reduces the amount of nickel holding the diamond particles 66 to the plate 62. The diamond particles 66 can thus break away from the nickel layer 64 and remain on the planarizing surface 42 after the conditioning cycle. The residual materials from the conventional conditioning stones 60 that remain on the planarizing surface 42 may produce defects on the substrate assemblies 12 during the planarizing cycle. Moreover, the loss of diamond particles 66 from the conditioning stones 60 changes the abrasiveness of the conditioning stones 60, which can cause inconsistent conditioning of the planarizing surface 42. Thus, there is a need to improve conditioning systems and processes to condition polishing pads 40.
The present invention is directed toward conditioning systems and methods for conditioning polishing pads used in mechanical and chemical-mechanical planarization of microelectronic-device substrate assemblies. In one aspect of the invention, a conditioning system includes a conditioning element or conditioning member having a conditioning face configured to engage a polishing pad. The conditioning face preferably includes a bonding medium covering at least a portion of the conditioning face and a plurality of conditioning particles attached to the bonding medium. The conditioning system also includes a corrosion-inhibiting unit that can be coupled to the conditioning element and/or a liquid on the polishing pad. The corrosion-inhibiting unit preferably retards corrosion of the bonding medium in the presence of chemicals on the polishing pad that would otherwise corrode the bonding medium. For example, the corrosion-inhibiting unit can be a DC power source coupled to the conditioning element to impart an electrical potential between the conditioning element and the polishing pad that retards corrosion of the bonding medium and/or other components of the conditioning element.
The conditioning system also preferably includes an arm to carry the conditioning element and an actuator coupled to the arm to selectively position the conditioning element with respect to the planarizing surface of the polishing pad. In operation, the actuator drives the arm to press the conditioning face of the conditioning element against the planarizing surface of the polishing pad, and then the conditioning element and/or the polishing pad move relative to one another to rub the conditioning element against the planarizing surface. As the conditioning element engages the polishing pad, the corrosion-inhibiting unit preferably applies an electrical potential to the conditioning element that retards corrosion of the conditioning element in the presence of the chemicals on the polishing pad.
The polishing pad is preferably conditioned during a discreet conditioning cycle between planarizing cycles of separate substrate assemblies. As such, another aspect of the invention is planarizing substrate assemblies by first removing material from the substrate assemblies using the polishing pad in the presence of a planarizing solution, and then conditioning the planarizing surface of the polishing pad by rubbing the conditioning element against the planarizing surface while retarding corrosion of the conditioning element.